Here are metadata describing the service and its data. They are known as the VOSI (Virtual Observatory Support Interfaces) resources. You use these metadata when registering your service and clients can read them to work out how to drive the service.
The resources come in two forms: split up by data collection or with all collections aggregated. In DSA/Catalogue, "data collections" are "catalogues". If you only have one catalogue then the two forms are equivalent. If you have multiple catalogues, then you can choose whether to register one service for all of them or separate, virtual services for each catalogue.
The availability of a data collection is the same as the availability of a service, so there are no per-collection links.
If you register with an AstroGrid publishing-registry, you pass it one of the links in this section when it asks for "URL for getting service capabilities". It will then find the other infomation for itself.